1. Field of the Invention
The present invention generally relates to a chip package structure, in particular, to a microelectromechanical system (MEMS) package structure.
2. Description of Related Art
Microelectromechanical system (MEMS) is a microelectromechanical device fabricated in a microminiaturized package structure, and the fabricating technique thereof is quite similar to the technique of fabricating integrated circuits (ICs). However, interactions, for example, about mechanics, optics, or magnetic force between the MEMS device and surrounding environment are more than that of the conventional IC.
The MEMS device may include micro-sized electromechanical components (for example, switches, mirrors, capacitors, accelerometers, sensors, capacitive sensors, or actuators etc.), and the MEMS device may be integrated with the IC in a manner of single block, thereby greatly modifying insertion loss or electrical isolation effect of the overall solid-state device. However, in the macroscopic world of the entire package structure, the MEMS device is extremely weak and may be impacted by slight static electricity or surface tension at any moment to cause failure. Therefore, in order to prevent the MEMS device from contaminations or damages, usually the MEMS device is sealed in a cavity between the wafer and the lid.
FIG. 1 is a schematic view of a conventional MEMS package. Referring to FIG. 1, a cover plate (lid) 110 is fixed on a wafer 100 with a sealant 112, such that MEMS devices 104 are sealed in a cavity 106 between the wafer 100 and the cover plate 110. Next, the wafer 100 and the cover plate 110 are cut into independent units, such that the MEMS devices 104 are sealed in the independent MEMS structures. The MEMS devices 104 are protected in the cavity 106, so as to ensure that the MEMS devices 104 operate normally. Next, the MEMS structures are sealed with an encapsulant (not shown), and thus the MEMS package structure is completed.
However, when an organic polymer compound is used as the sealant 112 or the encapsulant, it is impossible to totally isolating the moisture. After a long time, the airtightness of the sealant 112 or the encapsulant becomes worse, thereby affecting the normal operation of the MEMS devices 104.